Tetraspanins are small membrane-bound proteins that are expressed in species ranging from sponges to mammals, with each organism expressing a large number of tetraspanin family members. A. Garcia-Espana et al., Appearance of new tetraspanin genes during vertebrate evolution, Genomics (91), 326-334 (2008). Tetraspanins are typically involved in multiple biological processes, such as fertilization, parasite and viral infection, synaptic contacts at neuromuscular junctions, platelet aggregation, maintenance of skin integrity, immune response induction, metastasis suppression, and tumor progression. Tetraspanins cross the membrane four times, but not all four-transmembrane molecules are tetraspanins. In general, tetraspanins have short amino- and carboxy-terminal tails, a small intracellular loop between transmembrane region 2 (TM2) and TM3, a small extracellular loop (EC1) between TM1 and TM2 and a large extracellular loop (EC2) between TM3 and TM4, as illustrated in FIG. 1. See M. Zoller, Tetraspanins: push and pull in suppressing and promoting metastasis, Nature Reviews Cancer (9) 40-55 (2009).
In addition to having these various functionalities within the cell and at the cell membrane, large numbers of tetraspanins are also released from the cell in exosomes. A. Lakkaraju & E. Rodriguez-Boulan, Itinerant exosomes: emerging roles in cell and tissue polarity, Trends Cell Biol. (18), 199-209 (2008). Exosomes, 30-100 nm vesicles, are released by many cells. J. S. Schorey & S. Bhatnagar, Exosome function: from tumor immunology to pathogen biology, Traffic (9) 871-881 (2008). Exosomes derive from multivesicular bodies, which either fuse with lysosomes or fuse with the plasma membrane and release their intraluminal vesicles as exosomes. The molecular composition of exosomes reflects their origin from intraluminal vesicles and includes several tetraspanins. Id. Exosomal proteins maintain their functional activity, as shown by their capacity to present peptides in major histocompatibility complex class I and II molecules. Id. Exosomes are thought to constitute a potent mode of intercellular communication that is important in the immune response, cell-to-cell spread of infectious agents, and tumour progression. Tetraspanins and their associated proteins are enriched in exosomes. Although the contribution of tetraspanins to the make-up of exosomes is well known, their impact on the functions of exosomes has not been determined. However, some current research has shown that, potentially, a blockage of angiogenesis-initiating exosomes from tumors may hinder tumor vascularization and thrombosis. I. Nazarenko et al., Cell Surface Tetraspanin TSPAN8 Contributes to Molecular Pathways of Exosome-Induced Endothelial Cell Activation, Cancer Research (70) 1668-1678 (2010); see also H. G. Zhang & W. E. Grizzle, A Novel Pathway of Local and Distant Intracellular Communication that Facilitates the Growth and Metastasis of Neoplastic Lesions, American Journal of Pathology (184) 28-41 (2014).
Tetraspanin 8 (TSPAN8), otherwise known as CO-029, regulates cell motility and cell survival and is generally involved in the promotion of angiogenesis. Moreover, evidence exists that TSPAN8 promotes motility mostly through its association with α6β4 integrin. Research has shown that the interaction between TSPAN8 and α6β4 integrin induce changes in cell shape towards a migratory phenotype, increased motility, and hepatic metastasis formation. S. Huerta et al., Gene expression profile of metastatic colon cancer cells resistant to cisplatin-induced apoptosis, International Journal of Oncology (22) 663-670 (2003) and M. Herlevsen et al., The association of the Tetraspanin D6.1A with the α6β4 integrin supports cell motility and liver metastasis formation, Journal of Cell Biology (116) 4373-4390 (2003).
TSPAN8 has been reported to have a role in cancer. In particular, overexpression of TSPAN8 was originally noted in colorectal cancer and was subsequently identified in pancreatic cancer and hepatocellular carcinoma. M. Zoller, Gastrointestinal tumors: metastasis and tetraspanins, Gastroenterology (44) 573-586 (2006). In particular, TSPAN8 overexpression generally correlates with poor differentiation and intrahepatic spread of hepatoma and only a hepatoma clone that overexpresses TSPAN8 develops metastases. K. Kanetaka et al., Possible involvement of tetraspanin CO-029 in hematogenous intrahepatic metastasis of liver cancer cells, Journal of Gastroenterology and Hepatology (18) 1309-1314 (2003). In addition, increased TSPAN8 expression in a metastasis versus the primary tumor-derived colon carcinoma line further supports a role in tumor progression. S. Huerta et al., Gene expression profile of metastatic colon cancer cells resistant to cisplatin-induced apoptosis, International Journal of Oncology (22) 663-670 (2003). Furthermore, research has also shown that high expression levels of TSPAN8 are associated with increased resistance to apoptosis. S. Huerta et al., Gene expression profile of metastatic colon cancer cells resistant to cisplatin-induced apoptosis, International Journal of Oncology (22) 663-670 (2003) and S. Kuhn et al., A complex of EpCAM, claudin-7, CD44 variant isoforms, and tetraspanins promotes colorectal cancer progression, Molecular Cancer Research (5) 553-567 (2007). Other research has shown a similar relationship between increased expression of TSPAN8 and multiple forms of cancer. Q. Guo et al., Tetraspanin CO-029 inhibits Colorectal Cancer Cell Movement by Deregulating Cell-Matrix and Cell-Cell Adhesions, PLoS One (7) e38464 (2012) and O. Berthier-Vergnes et al., Gene expression profiles of human melanoma cells with different invasive potential reveal TSPAN8 as a novel mediator of invasion, British Journal of Cancer (104) 155-165 (2011). All references recited above and herein are hereby incorporated by reference in their entireties for any and all purposes.
A need exists for anti-TSPAN8 antibodies having unique genetic and amino acid structures, including unique binding and functional characteristics. The development of new anti-TSPAN8 monoclonal antibodies and hybridoma cells lines that produce such monoclonal antibodies would be a valuable tool for the effective diagnosis of various diseases and use in other biomedical techniques.